Maleic anhydride cannot normally be polymerized into polymers utilizing standard emulsion polymerization techniques. This is because the maleic anhydride hydrolyzes to the acid form in the presence of water wherein the polymerization process occurs and the resulting resin yields different characteristic physical properties than those desired. For this reason, polymers containing repeat units which are derived from maleic anhydride are normally synthesized in a solution polymerization process. Such solution polymerizations are generally carried out in an organic solvent which is inert with respect to the monomers being polymerized and the polymer being prepared.
It has been determined that polymers containing a vinyl aromatic monomer, an alkyl acrylate monomer, and maleic anhydride are of great value as electrostatic image developing toners. This is because the repeat units therein which are derived from maleic anhydride act as a built-in charge control agent. This eliminates the necessity for adding separate charge control agents, such as lacmoid (resorcinol blue), to the toner resin.
The possibility of synthesizing such polymeric resins, which contain repeat units which are derived from maleic anhydride, is attractive for numerous obvious reasons. For instance, the need for utilizing an inert organic liquid as the solvent for the polymerization and the costs associated therewith are eliminated.